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Wednesday, June 30, 2010

Note: Summer is the time for my field work, so updates to this blog will be less frequent for the next two months.

In the last blog entry, I discussed a mission concept being investigated by the Decadal Survey to place a lander on the Venus highlands (the tessera) called VITaL. This entry explores a second mission concept, the Venus Mobile Explorer (VME). In many ways VME is similar to the Venus tessera lander -- they both target the highlands and they both carry nearly identical compliments of instruments. While VITaLwould land at a single site, VME would land at one site, inflate a "balloon", float in the wind a few kilometers above the surface, and then land at a second site. This would allow imaging of a traverse of 8-16 km before settling at the second site. The imaging traverse and landing at two sites would help determine the diversity of the highlands, which may be remnants of ancient crust. Like the ViTAL mission, the VME mission was recently described in a paper presented at the 7th International Planetary Probe Workshop.

Since the instruments for the two missions are nearly identical (please see the VITaLdescription), I'll concentrate on the differences between the two missions in this entry. I used the term "balloon" in quotes above because "bellows" would be a more appropriate term. In the harsh conditions at and near the surface of Venus, traditional balloon materials cannot be used. Instead, VME would inflate a bellows system with helium to create lift and allow the lander to lift off and drift for approximately 4 hours before the second landing. At either a preset time or when internal temperatures within the probe rise above a preset limit, the bellows are discarded. The bellows cannot be deflated and then reused a second time because of plastic deformation of the metal in them during their first use.

The goal of the 25 Decadal Survey mission studies is to (1) scope out the concepts since many were ill defined at the start of the Decadal process, a problem that caused substantial cost under estimation in both the last astronomy and planetary Decadal Surveys; (2) determine the technological maturity of the concepts; and (3) provide cost estimates of the leading concept missions. The Decadal Survey members will eventually select a small subset of the 25 missions that fit within the budget, are (or can be in the next decade) technically mature, and that are most likely to provide the greatest advance in our understanding of the planets and their histories.

In keeping with the goals of assessing mission concepts, the authors of the VME paper list several issues with this concept:

1) The lander would need to survive the harsh conditions of the surface and near-surface for almost 5 hours (including time to transmit data up to the telecommunications relay), compared to the two hours for the VITaLconcept and three hours for the proposed SAGE Venus lander New Frontiers mission proposal. This leads to challenges in ensuring the interior of the lander remains cool enough to operate, increasing the cost of the mission.

2) The design of the bellows, the helium tank, and other mechanisms will be challenging and these elements require additional technological maturity before they can be used, adding to mission cost and risk.

3) The estimated cost of the mission without launch vehicle is $1.7B and with launch vehicle is $1.9B. [Editorial note: It often hard to compare mission proposal costs since details of what are included and excluded from costs often aren’t detailed. The cost of the SAGE lander is presumably within the $650M cap for the spacecraft portion of New Frontiers missions. However, the fully burdened cost of New Frontiers missions is approximately $1.2B, which includes the cost of the launcher and other overheads for running the New Frontiers program.]

Editorial Thoughts: Unless Venus exploration is given a high priority in the Decadal Survey process, the $1.7B price tag for this mission plus its technical immaturity would seem to make its selection unlikely. The authors of the VME study point out that they believe that "the bellows mobility concept is likely one of the lower cost ways to visit two different landing sites, though it has a higher risk versus multiple heritage [e.g., multiple SAGE or VITaLsingle location landers]." For the same launch mass and volume, two to three heritage landers could be delivered to Venus, although the authors do not provide a cost estimate. I have read that additional spacecraft of identical design cost ~50-60% the cost of the first spacecraft. So, if the SAGE spacecraft is ~$650M, then a second copy might be in the range of $325-375M. This back of the envelope analysis suggests that two to three heritage landers could be flown within the cost envelope of VME with lower technical risk.

On another topic, the VME paper makes clear why current Venus lander concepts are proposing to use laser-based remote sensing of the surface instead of direct analysis. To measure the surface material with any finesse, a sample needs to be brought into the lander where the instruments can be kept cool. The sampling mechanism for bringing in the surface material would weigh ~4 kg and the analysis would require a minimum of 2 hours. Sampling multiple locations with a laser (for illuminating the surface for Raman spectroscopy and vaporizing it for induced spectroscopy would require ~15 minutes. Reducing surface measurement time by an hour and 45 minutes should substantially reduce mission risk.

Closing note: The VME paper provides one of the most succinct summaries of the goals for Venus landers that I've seen. Measurements of the atmospheric composition are equally important as measurements of surface composition to meeting the full suite of goals. I'm quoting the entire list here:

1) determine whether Venus has a secondary atmosphere resulting from late bombardment and the introduction of significant outer-solar system materials, including volatiles, 2) characterize major geologic units in terms of major elements, rock forming minerals in which those elements are sited, and isotopes, 3) characterize morphology and relative stratigraphy of surface units,4) determine the rates of exchange of key chemical species (S, C, O) between the surface and atmosphere,5) place constraints on the size and temporal extent of a possible ocean in Venus’s past, 6) characterize variability in physical parameters of the near surface atmosphere (pressure, temperature, winds), and 7) measure the ambient magnetic field from low- and near-surface elevations.

Link to Venus Mobile Explorer paper. My thanks to Lori Glaze, lead author of the paper, for her assistance in writing this summary of the mission analysis.

Tuesday, June 22, 2010

Note: A previous version of this entry had the lander crashing onto the surface at 32 km/second -- that should have been a much gentler 32 km/hour (or 9 m/second * 3600 seconds in an hour / 1000 m in a kilometer). I apologize for the mistake.

Sunday, June 20, 2010

Note: A previous version of this entry had the lander crashing onto the surface at 32 km/second -- that should have been 32 km/hour (or 9 m/second * 3600 seconds in an hour / 1000 m in a kilometer).

The Decadal Survey is exploring 25 mission options (at last report) for possible inclusion in the next decade of planetary missions. (See the complete list of concepts in this blog entry.) Each mission is initially scoped out by a team at one of NASA's centers or John Hopkin's Applied Physics Laboratory to understand the technical requirements. An independent firm then assesses the likely costs of the mission. The results of two concept studies have recently been published as part of the proceedings of the 7th International Planetary Probe Workshop. In this entry, I'll describe the Venus Intrepid Tessera lander (VITAL) concept, and in the next entry I'll describe the Venus mobile explorer concept.

In many ways, the proposed tessera lander sounds much like the Venus SAGE lander currently in competition for the next New Frontiers mission slot. While details probably differ between the two proposed missions, what we learn from the from the VITAL concept probably also applies to the SAGE proposal

Broadly speaking, the Venusian surface is covered by extensive plains (which make up the largest portion), large shield volcanoes, the tessera. The latter are continent-sized regions of highly deformed, folded terrain. The origin of the tessera is unknown, although there is speculation that they may represent the oldest terrain on Venus. Measurement of the composition of the tessera is a high scientific priority. (By contrast, the SAGE mission would go to recently identified terrain on the flanks of a volcano that may be among the youngest terrain on Venus.)

In the past, it's been assumed that the tessera were off limits to landers because the steep terrain would prevent a safe landing. For this concept study, it was assumed that the slope might be as high as 30 degrees and that the lander might partially sit on a a large rock, creating further tilt. To deal with these conditions, the probe's pressure vessle is mounted above a heavy outer ring that lowers the center of gravity to provide stability in case of extreme tilt of up to 72.7 degrees. The lander uses drag plates to slow its descent through the dense lower atmosphere and hits the surface with a speed of 32 km/hour. The thermal system is designed to allow the probe to function during the one hour descent and for two hours on the surface.

Example sampling area for the Raman/LIBS instruments and context imaging.

A decade ago, it was assumed that high quality compositional measurements of the Venus surface would require a complicated sampling mechanism that would deliver samples to instruments inside the probe through an airlock. Today's mission concepts instead rely on lasers to illuminate or melt the surface materials with the results analyzed via spectrometry. (The Mars Science Laboratory's ChemCam will use this technique at Mars.) Using lasers and spectrometers greatly simplifies the probe design since only a window is needed to access the surface. The laser will operate in two modes. In a low power mode, it will illuminate the surface for analysis by a Raman spectrometer. At higher power, the surface material is vaporized for laser induced breakdown spectrometry (LIBS) and the resulting plasma is spectrally analyzed. Analysis is carried out across a 0.86 m row of spots each 0.3 mm approximately two meters from the lander. A camera will take high resolution context images of the sampling area.

Another key goal of the mission is analysis of the atmospheric composition during the descent and on the surface. A neutral mass spectrometer and a tunable laser spectrometer will perform these tasks. Another set of instruments will measure the physical charateristics of the atmosphere such as temperature and pressure during the descent.

Two camera systems will provide context images of the landing site. The descent camera will take a series of nested panchromatic images as the probe nears the surface. The panoramic imager will take color and near infrared images of the surface in four directions to image a total of 240 degrees of the horizon.

Comparison to the SAGE proposal: Only limited information on the SAGE mission has been publicly released (see this blog entry for a summary). At the summary level, the two missions seem very similar. They would carry nearly identical instrument sets, although the SAGE mission apparently would have an arm that could dig a trench to allow the laser to shoot targets 3-10 cm below the surface. The SAGE lander would be designed to survive for three hours on the surface.

The two missions are so similar that if the SAGE mission is selected for the next New Frontiers mission, many aspects of its design likely could be reused for a tessera mission. No cost estimate is given for the VITAL proposal, but it would seem that if the SAGE mission can be flown within the cost cap of the New Frontiers mission (~$650M for the spacecraft and another ~$550M for other costs), then the VITAL mission could in a similar ballpark, and perhaps less if it can reuse substantial portions of the SAGE design.

Wednesday, June 16, 2010

A previous post looked at the proposed AVIATR Titan plane proposal. This mission, which is currently contending for the next Discovery mission slot, would use an airplane to study the surface and atmosphere of Titan. Unlike previously proposed balloon missions that would drift with the winds, this mission would be able to send the plane to survey specific surface targets such as river systems, lakes, and mountains. The plane would be able to fly faster than Titan rotates, so that it would always remain on the sunlit, Earth-facing side of Titan.

Compared to previously proposed balloon missions (both the 2006 $1B Box study and the Titan Saturn System Mission (TSSM) proposal), this mission has some compromises. The science payload is about half of what the balloons would have carried (see table below). Some key instruments such as a mass spectrometer to study atmospheric composition and a radar sounder are not included in the AVIATR proposal. The TSSM balloon mission would have returned far more data, but that was contingent on the presence of a flagship orbiter to relay data. The data rate of the AVIATR mission appears to be similar to that of the $1B Box study balloon platform, which would have sent data directly to Earth. However, almost twice as much data would be returned by AVIATR because the balloon would spend half its time facing away from Earth when it would have been on the night side of Titan.

Instruments proposed for the AVIATR plane and the TSSM balloon platform

On the other hand, being able to actively manuever gives AVIATR some key advantages over a balloon. When AVIATR reaches a target location, it can climb high and fly a grid pattern to take context images of the entire area. Then it can drop down to ~3.5 km to take high resolution images of portions of the area.

To make the most use of the 2GB of data return, AVIATR would send thumbnail images back to Earth. Scientists would then select the most interesting images for full transmission, and AVIATR would use data compression to make maximum use of the bandwidth. A similar scheme was used for the Galileo mission, which had to deal with a similarly constrained data rate due to a malfunctioning antenna.

The cost of the AVIATR mission is described as either Discovery class (~$800M) or New Frontiers class (~$1.2B). (These are fully burdened costs derived from dividing the proposed decadal budget for these programs by the number of expected missions. The costs include the ~$450M and ~$650M, respectively, allocated to the principal investigator plus launch vehicle and presumably other overhead.) The $1B Box study estimated the cost a standalone balloon mission at ~$1.4B using what appears to be similar accounting methods but in FY06 dollars.

Editorial Thoughts: I do believe that we should continue the exploration of Titan and Enceladus in the coming decade. Currently, the flagship mission slot is given to the Jupiter Europa Orbiter over the Titan Saturn System Mission (a decision I agree with, but one the Decadal Survey could overturn). In my opinion, portions of the TSSM proposed mission should be flown: An Enceladus multi-flyby (and possible orbiter) mission that would also study Titan in a series of flybys, a Titan lake lander a la the proposed TIME mission, and either a Titan balloon or airplane mission. There are indications that all of these components individually could be in the Discovery to New Frontier mission class. Ideally, this would be an international effort with more than one space agency contributing the mission elements. I would like to see the balloon or plane carried to Titan by the Enceladus Saturn orbiter that would also act as a data relay and enable substantially more than 2GB of data to be returned.

If a balloon or plane mission were to be flown, I'd prefer the plane mission. The plane could better study the surface by flying to chosen locations of high interest rather than depending on the fate of wind direction. To partially make up for the limited atmospheric instruments in the plane mission, the Titan lake lander could perform atmospheric chemistry measurements during its descent.

Sunday, June 13, 2010

In this blog, I normally try to stay away from advocacy in the belief that there are already plenty of blogs that focus on political advocacy. In this instance, I will break that rule and suggest that if you are an American citizen, that your write your senators and representative to encourage funding for the restart of Plutonium-238. (If you aren't an American citizen read on anyway, there's some interesting information here.) This is in a support of a letter writing campaign being initiated by the Division for Planetary Sciences of the American Astronomical Society. Their site provides a suggested letter and a related site provides background on the Pu-238 problem. Last year, Congress deleted proposed funding for the restart from the budget. The planetary science community appears to be concerned that the same could happen again this year.

The chart below neatly summarizes the problem. NASA has depended on Pu-238 to power missions whereever sunlight is irregular (lunar stations), faint (the outer solar system beyond Jupiter), or solar power is impractical (the Viking landers and the Mars Science Laboratory). Unfortunately, the United States has not produced new Pu-238 supplies for over two decades, and stockpiles are running low. Russia had been selling its Pu-238 stockpile to the United States, but has cancelled the contract. Even if the contract is renegotiated (and I've not seen any news on this since last December), NASA would have sufficient Pu-238 for an upcoming Discovery mission, the Jupiter Europa Oribiter, and one other small mission (the chart below lists the Intenational Lunar Network mission, but the Decadal Survey may or may not priortize that mission over other missions).

Without the Russian Pu-238, NASA would have to power the Jupiter Europa Orbiter using a new, yet-to-tested-in-flight ASRG power source that could use roughly one quarter the Pu-238 currently planned for the mission. NASA, however, is reluctant to bet a $3B+ mission on untried technology. By my reading of the situation, if NASA were to take the gamble, it would have sufficient Pu-238 for that mission and perhaps an additional Discovery-class mission beyond the two small missions included on the chart.

Without a restart of Pu-238, a future flagship Titan orbiter might not be able to fly (solar panels for that class of mission at Saturn would be enormous, although smaller orbiters could use solar panels). Long-lived missions to explore the atmosphere and surface of Titan require Pu-238. The proposed Argo mission to Neptune, Triton, and a Kuiper belt object also would require Pu-238 as would the Titan Mare lander, the Titan AVIATR plane, the Io Volcano Observer, a lander that moves to different locations on a comet's surface, and a Trojan asteroid multiple flyby-orbiter-lander. Several missions would be enhance by a Pu-238 power supply including a proposed comet coma sample return, a Mars polar lander, Venus balloon platforms, and probably many missions we've yet to hear of.

Editorial Thoughts: I've said in previous blogs that the most important decision facing the Decadal Survey is whether or not to prioritize a Mars sample return mission (which likely would require nearly half of NASA's planetary program). The second most important decision may be which missions to prioritize in the face of a finite Pu-238 supply -- Congressional funding is not guaranteed. The next Discovery mission may be powered by an ASRG (I think it will probably be; I think NASA would want to have the technology flight tested). If the Jupiter Europa Orbiter flies with ASRGS and there's no future production, then there will be sufficient Pu-238 for just a few, maybe one or two, Discovery-class missions. Which to prioritize would be a key question. My vote would be for in-situ missions to Titan and perhaps Argo, but many worthy targets deserve consideration.

If budgets are cut, existing planetary exploration budgets may or may not be targeted. However, if agency budgets are cut, it seems unlikely that new funding would be added to planetary exploration budgets.

Tuesday, June 8, 2010

The latest print issue of Aviation Week and Space Technology has a one sentence mention that budgetary concerns will push the earliest flight of the Mars sample return from 2020/22 to 2022/24. Presumably, the MAX-C caching rover/ExoMars rover remains on track for 2018 and the elements that would be pushed back are the Mars orbiter-Earth return vehicle and the Mars lander-ascent vehicle that would deliver the samples to the orbiter-return vehicle.

There has also been a splash of coverage about the possibility of life on Titan (see this MSNBC article as an example or this more sensational article from the Telegraph or the original press release). Like the discovery of methane on Mars, the news isn't the discovery of life but rather the composition of the atmosphere that indicates that life could be present. In the case of Titan, it's the absence of chemicals in the atmosphere that could be compatible with the presence of a methane-based life on Titan. Chris McKay, who has proposed that the absence of these chemicals could be a sign of life, warns that life remains the least probable explanation for the data and computer modeling. His essay makes interesting reading (Have we discovered evidence for life on Titan?).

As an editorial note, whether to proceed with the work necessary to enable a Mars sample return in a decade or so probably remains the key decision for the Decadal Survey. A sample return on this schedule probably requires that the Mars program continues to consume a bit less than half the planetary program budget. If that continues, then there is not enough money to fly both the envisioned rate of Discovery and New Frontiers missions and the Jupiter Europa Orbiter. The reports on Titan's atmospheric chemistry works makes Titan an even more interesting place to explore. The Discovery-class Titan Mare Explorer could shed light on these issues, but I believe it would have to be selected in the current Discovery selection to fly in time to land on the lakes while they are in view of the Earth. Of course, Titan and Enceladus deserve more attention than a single Discovery-class mission in the coming decade than this, but as noted above, the budget just doesn't go far enough to do all the missions that should be flown.

Let me know in your comments if you would be interested in seeing the budget consequences of funding either JEO or a Titan/Enceladus mission.

Sunday, June 6, 2010

The SPA basin lies almost entirely on the far side of the moon. MoonRise would be the first mission to collect samples from that hemisphere. In this topographic map, red indicates high elevations while purple indicates low elevations. From Wikipedia based on Kaguya data.

Late last year, NASA announced three finalists in the selection for the next New Frontiers mission. Two of the three missions, the SAGE Venus Lander and the OSIRIS-REx asteroid sample return mission have previously been discussed in this blog. This time, I'll describe the goals for the third finalist, the lunar MoonRise South Pole-Aitken (SPA) basin sample return.

Unfortunately, I largely will only be able to describe goals. As with most mission proposals for the New Frontiers and Discovery programs, the proposing teams are keeping the implementation details to themselves. It's common for these missions to be proposed several times, and there's no point to giving potential competitors ideas. We do know that a single lander is being proposed (unlike a previous New Frontiers proposal to sample the SPA basin) and that there will be a communications satellite. The goal is to gather 1 kg of lunar soil, which is expected to contain 10,000 2-4 mm particles, >3,000 4-10 mm framents, and "a significant number" of small rocks >1 cm. Because large impacts spread material across the lunar surface and small impacts churn the local soils, it's believed that a single soil sample will sample a diversity of sites from within the basin. Thanks to the plethora of satellites that have and are studying the moon, the proposers think that they can pick a site to optimize the value of that heterogeneous soil sample. No rover would be needed to collect samples.

That's the what of the mission, but what about the why of the mission? The SPA basin is the largest of the impact craters on the moon (and possibly the solar system) and was one of the earliest of the large lunar impacts (see Wikipedia article). It is so large, that several later good sized impacts lie within it. One of the key questions for the early history of the terrestrial planets has been the nature of the large bombardments of the planets near the end of their formation. There's a debate about whether there was a single dramatic pulse of impacts or whether they were more spread out over time. Samples from the SPA basin can date the impacts within the basin. Coupled with information on the dates of impacts elsewhere on the moon from samples collected in the 1970s, this mission could help to resolve this debate or take it in new directions.

A second goal for this mission is to use the samples to better understand the effect the initial and subsequent impacts had on the development of early planetary crusts. Samples will allow us to determine how deeply the impacts penetrated the crust, the thermal state of the moon at the time of impact, and provide ground truth for the remote sensing data on the current surface of the basin.

The third goal is to use the basin to collect samples from various depths of the lunar crust and possibly mantel. The cumulation of large impacts within the basin means that samples are likely to have been thrown up from various depths beneath the surface. Understanding how terrestrial planets differ with depth and across their surface has long been a goal of terrestrial and planetary science.

You can read about the goals of this mission in much more depth in the two following two-page abstracts from the last Lunar and Planetary Science Conference:

Editorial Thoughts: The New Frontiers selections are highly competitive and it's not surprising that three finalists are all scientifically strong. Any one of them will make a significant contribution to planetary science. OSIRIS-REx would provide a major boost to the study of primitive bodies in the solar system and would build upon a number of previous missions and compliment the Rossetta comet mission. SAGE would re-invigorate the study of the Venus surface and could be an American contribution to a series of missions to study Venus from several space agencies. MoonRise would provide ground truth for the number of missions that have recently flown to the moon and the several that are planned in the coming decade.

Given that the science potential of all these missions would be high, the final selection is likely to be made on the basis of technical maturity, costs, and programmatic risks. Unfortunately, the public has no insight into these issues and therefore has no way to handicap the selection. The current date for the selection is April or May of 2011.

Friday, June 4, 2010

The Falcon 9 maiden flight was a success (see AWST article). This is one of the launchers that NASA is depending on for future low- and mid-range cost science missions. (See background here.) NASA will also use the Falcon 9 to deliver supplies to the International Space Station.

Tuesday, June 1, 2010

Note: I'm not sure what happened to the fonts in this post. They look fine in the the blog site's editor and preview. I'm hoping that the simple edits I tried this morning have helped to solve the problem.

Aviation Week and Space Technology reports that the proposed Precursor Mission budget might be raided to pay for other manned spaceflight missions. (Read a description of the proposed program at http://futureplanets.blogspot.com/2010/05/robotic-precursor-missions.html.) In a subscription-only article, AWST reports that NASA is revising its FY11 manned spaceflight budget. A Congressional analysis has concluded that the Administration's new program, AWST reports, is as underfunded as the previous Administration's program. As a result, " Administrator Charles Bolden conceded [at a Congressional hearing] what many critics have been charging for months -- that the open-ended exploration-technology program in the new budget will be raided to pay for other work, including the space station crew return vehicle (CRV)... and the heavy-lift launcher."

Editorial thought: The current vision for the Precursor Missions is ambitious. If the program budget is cut, I hope that sufficient funds remain to at least allow the investigation of one or more near Earth asteroids that might be a target of future manned spaceflight. This could both pave the way for a manned mission and provide useful science. There may also be opportunities to fund instruments on science missions. The scientific community has expressed concerns that the goals for the Mars Trace Gas Orbiter are ambitious given the budget; perhaps the Precursor Mission program could help fund instruments useful to both programs such as very high resolution cameras.

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Two articles report that Japan is planning to make the moon a focus of its planetary exploration. It plans to to land a mobile research station in 2015. That will be followed up with the establishment of an unmanned research station near the lunar south pole by the end of the decade. Among other goals, the station will return samples to Earth. Total investment over the coming decade could be over $2B.

Editorial note: Several space agencies have sent orbiters to the moon over the last few years. China and India are also planning lunar missions this decade. If all three nations carry out their plans, then the moon will receive the kind of focused exploration that Mars did in the last decade.

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AWST also published online its lead article from this week's issue on the Webb space telescope, and it is full of details on this mission and its development status: Webb Telescope to View Early Universe

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Astrobiology Magazine has an article describing work that suggests that Europa's oceans may have oxygen levels similar to those of our own oceans. If this is true, then it makes Europa a more enticing target for exploration since high oxygen levels could enable higher forms of life (at least microbial life). See Europa's Churn leads to Oxygen Burn.

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Space Review has an article on the chances that the Falcon 9 maiden launch will either fail or be only a partial success. Alan Stern reminds us that failure in early flights is common and what counts is the drive to continue to keep trying until the technology is proven. (This also suggests why NASA requires three successful flights of a launcher before committing a science mission.) You can see Alan's editorial here.

About Me

You can contact me at futureplanets1@gmail.com with any questions or comments.
I have followed planetary exploration since I opened my newspaper in 1976 and saw the first photo from the surface of Mars. The challenges of conceiving and designing planetary missions has always fascinated me. I don't have any formal tie to NASA or planetary exploration (although I use data from NASA's Earth science missions in my professional work as an ecologist).
Corrections and additions always welcome.